757
FXUS64 KLUB 011557
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
1057 AM CDT Wed May 1 2024

...New MESOSCALE UPDATE...

.MESOSCALE UPDATE FOR AFTERNOON SEVERE STORMS...
Issued at 1057 AM CDT Wed May 1 2024

Upper air analysis this late morning depicts a shortwave trough
digging into the north-central Rocky Mountains, with a well-defined
vorticity lobe rounding the base of the trough and beginning to
eject into the west-central Great Plains. Further south, a subtle,
shortwave perturbation was analyzed over northern Mexico, and was
steadily moving northeastward towards the Big Bend region while the
mid/upper-levels are otherwise bereft of any noticeable feature on
the water vapor bands. The 12Z objectively analyzed upper air data
depicted the left-exit region of the 250 mb jet eclipsing southern
New Mexico, evident by a 50 kt wind maximum observed on the EPZ RAOB
this morning while the primary jet streak near 80 kt was located
further south per the MMCU RAOB (Chihuahua International Airport).
Upstream RAOBs from ABQ and EPZ also indicated a substantial
elevated mixed layer (EML), and the 12Z AMA RAOB also sampled the
EML as the balloon was launched within the dryline circulation.
Meanwhile, the 12Z RAOB from WFO MAF sampled a large EML atop a
strong cap with mixed-layer parcels yielding >2,500 J/kg CAPE amidst
a very moist, yet shallow, boundary-layer, characterized by T/Td
spreads of only 6 degrees and a dewpoint of 67 degrees. This airmass
was, and continues, to advect northward where LIDAR data out of LBB
continues to detect the dispersion of a strong low-level jet (LLJ)
with a speed now <=30 kt compared to the near-50 kt LLJ sampled
earlier this morning.

At the surface, a lee cyclone with a minimum pressure of 1008 mb was
analyzed over the OK PH, particularly GUY, with a sharpening dryline
extending southwestward across the TX PH and into the extreme
southwestern TX PH as per recent West Texas Mesonet (WTM) and METAR
data. A reservoir of 60+ degree dewpoints exists to the east of the
dryline, with the 65 degree isodrosotherm delineated generally along
the I-27/HWY-87 corridor per WTM data. Dewpoints were approaching 70
degrees across the Rolling Plains as well, with a corridor of very
high theta-e air (e.g, 350-355 K) spread across the Caprock and
Rolling Plains this morning. Visible satellite imagery and webcams
reveal a shallow, low-level stratus deck anchored across the eastern
Rolling Plains with evidence of billows across the Rolling Plains
while a shallow cu field continues to develop and advect northward
from the Permian Basin and into the CWA. The billows have been
convectively reinforced by outflow from severe convection last
night, though the increase in pressure tendencies following the
passage of the initial gravity waves were negligible and pressure
tendencies have since stabilized. Differential heating along the
edge of the stratus deck was most pronounced across the far
southeastern TX PH where current temperatures are in the upper 60s
while increasing into the middle 70s where the billow field is
located.

Deepening of the lee cyclone to the north will continue throughout
the rest of the day beneath the glancing influence of the shortwave
trough ejecting into the west-central Great Plains today, with most
guidance indicating gradual pressure falls of 10 mb/12 hr through
00Z this evening. The pressure falls associated with this deepening
cyclone will generate an isallobaric response such that the
southeasterly winds within the moist sector accelerate to 15-25 mph
with gusts to 35 mph this afternoon and evening. The dryline bulge
remains positioned to the north of the CWA at this time, and the
combination of intense, diabatic surface heating as temperatures
breach 90 degrees along the I-27/HWY-87 corridors and into the upper
80s in the Rolling Plains; intensifying low-level storm-relative
inflow, and the continued advection of high theta-e air, will serve
as a focus for the initiation of a discrete supercell or two in
close proximity to the extreme southeastern TX PH and northern
Rolling Plains. VWP data from the KFDR WSR-88D (despite the lapse in
data from maintenance) continues to observe a substantial component
of streamwise vorticity in the 0-1-km layer where storm-relative
helicity values are approaching 400 J/kg as of 1518Z.

A tornado threat is forecast to focus in proximity to the extreme
southeastern Texas Panhandle, including the City of Childress, late
this afternoon as convection unzips to the south in the form of a
broken MCS as CINH erodes from intense heating in congruence with
the belt of weakened mid-level flow. The best timing for this
scenario is 5-8 PM CDT (22Z-01Z) as discrete propagation,
particularly with a rightward-moving supercell, will be <=10 kt to
the southeast in environment of buoyant and unimpeded storm-relative
inflow, especially if the full component of the right-moving storm
motion vector is realized. Deviant tornado movement can be expected
in a situation such as described above, and with high relative
humidity within from the surface-to-700 mb layer, in addition to the
dampened storm-relative flow at anvil-level, hydrometeor loading of
updrafts will occur with HP supercells expected and would lead to
cyclic behavior of discrete/semi-discrete storms before upscale
growth occurs. Large, bulbous, rear-flank downdrafts would also
enhance the potential for wind-damage and further enhance deviant
tornado movement during the occlusion process. The slow storm motion
associated with right-moving supercells and excessive hydrometeor
loading also points towards both the potential for very large hail
near baseball size and/or a accumulating hail event as wet-bulb zero
heights were objectively analyzed near 8 kft AGL. An additional
discussion involving the forecast for the rest of the CWA will be
issued with the primary package this early afternoon as the
expectation for a broken line/MCS remains intact.

Sincavage

&&

.SHORT TERM...
(Today and tonight)
Issued at 311 AM CDT Wed May 1 2024

In classic West Texas fashion, the first day of May should hit the
ground running with dryline storms later today and especially by
this evening. Early morning water vapor imagery showed gravity waves
rolling west over the region courtesy of two MCSs in OK, but
otherwise our W-SW flow aloft was devoid of any meaningful features.
This will change later this morning as SW winds aloft pick up some
steam ahead of an elongated trough overspreading the Intermountain
West. At the surface meanwhile, a dryline roughly from Dora-Dimmitt-
Amarillo at 2 AM is expected to retreat another 60 miles or so ahead
of increasingly moist southerlies and eventually some low clouds by
daybreak. Eastward mixing of the dryline this afternoon doesn`t
appear particularly aggressive thanks to the deepening moisture and
more importantly a diffuse surface low drifting from eastern NM into
southeast CO by this evening. By peak heating, most high res
guidance paints the dryline along a line from Silverton southwest to
Lubbock and Brownfield which seems reasonable.

East of the dryline, MLCAPEs should soar to 2500-3500 J/kg with
modest CIN overall and 30-35 knots of deep layer shear. Marginal CIN
and poor anvil-level SR flow would tend to favor a shorter window
for supercells early on, before ample DCAPE near the dryline raises
the chances of storm modes becoming increasingly messy and linear.
On that note, several models (CAMs and globals) depict a H7 trough
currently along the Sierra Madres that lifts northeast through the
day before triggering dryline storms over the western Permian Basin
around 21Z and growing quickly upscale thereafter. Given large DCAPE
along the dryline and straight hodographs, there is a growing signal
from CAMs that this initially supercellular convection could be
quite efficient with downbursts and more importantly left movers
that race north and into our southern South Plains this evening
complete with damaging winds and blowing dust. Past events such as
this often accelerate the dryline`s evening retreat and expand
chances for additional storms. NBM`s westward extent of PoPs on the
Caprock look good for this setup, but its values were raised
considerably off the Caprock by this evening as a linear MCS is
likely to evolve with wind and heavy rain the greatest threats.

A second and more conditional area for storm initiation later today
could involve an outflow boundary currently loitering over our
northeastern counties from nocturnal storms in southwest OK. This
boundary appears rather diffuse overall and will more than likely
wash out through the day given how much modification will ensue in
the next 12+ hours. Convection should depart our eastern zones
toward midnight all the while the dryline returns to NM and a cold
front works its way south across the western TX Panhandle. NBM temps
today and tonight needed no change.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 311 AM CDT Wed May 1 2024

A generally quieter weather day is expected on Thursday as an early-
day cold front passes southward through the region. The front itself
will not be particularly strong or quick-moving as upstream pressure
rises remain modest and deepening surface troughing over eastern NM
and the Permian Basin slow its southward progression. Even behind
the front temperatures will still warm well into the 80s with the
more notable post-frontal change being a reduction in near-surface
moisture and relative lack of cloud cover given the drier upstream
airmass. Some models still depict isolated convection on Thursday in
the vicinity of a remnant dryline, but this should be well to our
east and will therefore carry a dry forecast over the entire
forecast area Thursday through early Friday. Guidance is in good
agreement that low level moisture will increase once again
beginning on Friday as surface flow obtains a stronger easterly
component, which will also result in high temperatures falling
back near seasonal averages. Thunderstorm potential on Friday is a
bit more unclear as some models hint at scattered storms firing
within the moist upslope regime, but large-scale forcing will
still be quite weak with only a very modest midlevel wave progged
to approach the region during the evening with inhibition also
appearing fairly significant due to a strong capping inversion.
Still, the uncertainty and increased moisture does support
maintaining low PoPs off the Caprock Friday afternoon and evening.

An additional cold front will pass through the region on Saturday,
with flow aloft also progged to strengthen through the day as well.
A majority of model guidance still points to the late Saturday
through early Sunday period as most favorable for potential
widespread rainfall as a more significant upper level disturbance
transits overhead within the stronger southwest flow aloft.
Specifics are uncertain at this range, but ensemble consensus
suggests that most of the region has a good chance (50-80%) of
receiving one tenth of an inch of rain or more over the weekend.
Early next week, a much deeper upper trough is progged to develop
over the western CONUS, but at this point its projected evolution
would bring a return of dry and breezy conditions to our area Monday
through Tuesday.

&&

.AVIATION...
(12Z TAFS)
Issued at 615 AM CDT Wed May 1 2024

Beginning to see MVFR visbys and lower CIGs develop from CDS on
north behind an outflow boundary, although it`s unclear if these
conditions will become prevailing or not. Satellite and models
suggest VFR is more likely to win out overall at CDS and also at
LBB where a second layer of stratus could threaten around sunrise.
Toward this evening, ISO TS should develop near LBB and grow in
coverage as they shift E-NE toward CDS. However, this threat is
still 12+ hours out and not worthy of a TS mention at the moment.

&&

.FIRE WEATHER...
Issued at 311 AM CDT Wed May 1 2024

Dry and breezy conditions are likely this afternoon across the far
southwest Texas Panhandle and northwest South Plains behind a
dryline. Fuels in these areas are more receptive to fire spread and
when combined with southwest winds of 15 to 20 mph and RHs falling
to around 10 percent, a Rangeland Fire Danger statement is justified
for Parmer and Bailey Counties from 1 PM until 8 PM. Farther east,
thunderstorms (some severe) will increase in coverage by this
evening with heavy rainfall possible off the Caprock.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

MESOSCALE UPDATE...09
SHORT TERM...93
LONG TERM....30
AVIATION...93